Clinically detectable cancers consist of a heterogeneous collection of cells differing in many characteristics including metastatic potential, immunogenicity and drug resistance. The generation of variant tumor cell populations from the original (clonal) neoplastic cell and the selection from these variants of more aggressive populations results in tumor progression. this process may be enhanced by the postulated genetic instability of the most aggressive variants. We hypothesize that inflammatory cells present in situ act on inherently genetically unstable tumor cell subpopulations to fuel progression. We have shown, previously, that macrophages can induce mutation in bacteria and can induce the appearance of drug resistant tumor cell variants. It is the intent of this proposal to determine (1) how macrophages can induce lesions in the DNA of tumor cells that can lead to progression and (2) whether inherent differences in tumor cell subpopulations exist as to the relative susceptibility to such activity. Studies by ourselves and others implicate reactive oxygen intermediates (ROIs) produced by macrophages as the likely candidates to induce lesions in the tumor cell DNA. A common action of ROI is to induce breaks in DNA backbone. Therefore we have employed the alkaline unwinding method and the alkaline elution method to assay DNA strand breaks (single and double strand and alkali-labile sites) in target cell DNA. We aim to continue to characterize this effect and to determine if murine mammary tumor cells at different stages of progression (i.e.) nonmetastatic vs. Metastatic) have different sensitivities to ROI-mediated strand breaks under conditions where repair is inhibited or permitted. If such differences in sensitivity are detected, we will determine if they are related to levels of protective enzymes such as superoxide dismutase, catalase or the glutathione redox cycle. We will continue to characterize the nature of macrophage-mediated DNA strand breaks. We have shown that co- incubation the nature of macrophages and tumor cells leads to the induction of significant numbers of strand breaks in tumor cell DNA. This activity is inhibitable by scavengers of ROI or some inhibitors of arachidonate metabolism. We will determine if this activity is dependent on the macrophage activation state, macrophage to tumor cell ratio, or the generation of products of the respiratory burst or arachidonate metabolism.